1. Field of the Invention
The present invention is related to an ion laser which is capable of producing light from a chosen group of wavelengths, said group of wavelengths not being available using lasers employing a single gas. More particularly, the present invention is related to a compact, continuous output, ion laser which employs a combination of gases, such as argon and krypton gases, such that a controlled laser output of multiple wavelengths can be produced by a single laser.
2. Background of the Invention
Lasers are used extensively in industry, science, and entertainment. It will be appreciated that lasers are found to be particularly useful because of their ability to produce a coherent beam of intense light. For many applications it is desirable to produce light having a certain dependable and reproducible wavelength.
One type of laser that has achieved widespread acceptance is the ion laser. Among other factors, the ion laser is often preferred because of its potential to be compact in size and inexpensive to manufacture. In essence, the ion laser operates by exciting a gas contained within a tube in order to produce an emission of photons of a particular discrete wavelength. In the typical ion laser, atoms are excited by electrical discharge to an excited ion state. The excited atoms, being inherently unstable, have a tendency to return to a lower energy state. Accordingly, photons of specific frequencies are emitted by the electrically excited atoms in order for those atoms to return to a stable energy state. During this process both heat and light energy are produced.
The basic ion laser consists of three primary components. These include a resonator, a laser tube (plasma tube), and a power supply. The resonator generally holds two reflective surfaces, such as mirrors, in alignment. The mirrors then define the "optical cavity" or the area in which the laser beam is generated. In the typical ion laser, one of the mirrors is essentially totally reflective of light in the desired wavelengths. This mirror is often referred to as a high reflector. The other mirror (output coupler), is partially transmissive of the subject frequency in order to allow a fraction of the light energy stored in the optical cavity to escape. The escaping energy constitutes the output laser beam.
The laser tube provides optical gain within the resonator, causing it to act as an oscillator of the desired light frequency. Among other factors, the gain provided by the laser tube depends on the reflectivity and dimensions of the resonator, the spacings and lifetimes of the energy states of the gas ions within the tube, the number of gas ions present per unit volume, the ambient temperature, the gas temperature, energy-state-related interactions between different types of ions when more than one gas is present, and the frequency, voltage, and direction of the electrical discharge which is impressed on the gas. The laser power supply provides electrons which may be used to excite gas ions in the laser tube, thereby stimulating emissions. Direct current provides a sustained arc discharge through the gas of the laser tube, thereby permitting a continuous laser discharge, unlike the pulsed output produced by excimer or most ruby lasers. To produce lasing, however, rather than mere radiation, the power supply must also ensure that the electrons provided have a particular frequency and direction.
In the discharge, the ionized atoms of the gas are excited through multiple collisions with accelerated electrons. As mentioned above, ion lasers often use noble gases such as krypton and argon in the laser tube. Thus, stimulated emission from the various excited states to the ground state of the ionized argon or krypton atom produces the required lasing action. Depending on physical conditions of the discharge, a fraction of the noble gas atoms may be double ionized. Stimulated emission from these states occur as well giving rise to multiple frequency output.
During operation of an ion laser, the photons emitted during an induced transition of the type mentioned above, have the same phase and direction as the inducing electron wave (i.e., they are coherent with the wave that induces the transition). A single atom may radiate a photon in any direction. However, many atoms distributed over a finite volume (within the laser tube), and radiating coherently, cooperate to generate a wave having the same propagation vector as the inducing wave, within the limits of a diffraction pattern. That is, they amplify the inducing wave.
Thus, the radiation from induced emission has a spectral distribution identical to that of the inducing radiation. It is found that certain types of atoms produce certain specific wavelengths of radiation during the energy transition and emission of photons. For example, argon, a common substance for use in an ion lasing medium, produces approximately nine primary wavelengths of radiation. The most commonly used wavelengths for laser purposes are at approximately 488 nm and 514 nm. Krypton, another gas used in ion lasers, also produces distinct wavelengths of radiation, including radiation at approximately 647 nm, 568 nm, 530 nm, and 520 nm. It will be appreciated that once a distinct wavelength of radiation is isolated, it can be used to produce a lasing action as it oscillates through the optical cavity.
For some applications, it is desirable to have more than a single output frequency and it is particularly useful to have output from the laser in both the blue wavelengths, and at least one other usable wavelength. For example, the combinations of blue and yellow and blue and red are found to be particularly useful.
One context in which multiple wavelength laser outputs are desired is in the area of scientific research. For example, it has been found that laser produced light is capable of causing certain microscopic structures to fluoresce after being stained with a selected dye. Certain structures fluoresce under blue laser radiation, while other structures fluoresce under red or yellow radiation. Thus, it would often be useful to have the capacity to direct laser produced light of multiple wavelengths onto a particular microscopic sample of interest. Thus, distinct structures could be simultaneously viewed, studied, and compared without the need to switch lasers or to focus multiple lasers.
Until now, however, it has been impractical to employ conventional lasers in this context. In order to make this type of use practical it is necessary to provide a laser which produces a constant output and which is sufficiently portable to attach to a microscope or similar apparatus. Known multiple output lasers, are very generally large, expensive and water cooled. Thus, it is impractical to use that type of laser in the context of a microscope.
Other problems, such as difficulty in adjustment and the production of different colored output beams of widely varying power also limit the usefulness of existing lasers. Employing known technology it is difficult to select output power, particularly where more than one frequency is involved, because output power depends on numerous parameters which are not easily adjustable in combination in previous systems. Thus, it would be an advancement in the art to increase control over the gas pressure, operating current (and discharge voltage), and relative percentages of each gas in the laser tube.
Laser beams of specific colors have also been found useful in the printing industry. In the area of color separation it is often desirable to have the capability of irradiating a piece of work with both red and blue light. Other colors may also be useful in certain situations. This reduces the number of steps and the complexity of the color separation process. Again, however, the limitations of existing lasers make the use of lasers in printing less than totally desirable, particularly since it is often necessary to use multiple lasers.
In the study of flow dynamics, lasers of particular wavelengths may have great usefulness. One technique which has employed lasers is "Laser Doppler Velocimetry." Using multiple colored laser light, it would be possible to obtain extensive data concerning flow dynamics and to track multiple variables. Such techniques would be useful, for example, in the production and design of aircraft. Thus, it will be appreciated that portable, constant output, ion lasers which could also produce multiple colored outputs would be very useful.
In order to achieve multiple colored laser beams of specific wavelengths, it is conventional in the art to employ multiple lasers. It has been found useful to provide an argon laser and a helium-neon laser together such that the blue produced by the argon laser and the red produced by the helium-neon laser will both be available.
Problems with this approach are obvious and have been mentioned briefly above. It is necessary to align two separate and distinct lasers. Alignment of the lasers is critical to the applications discussed above. Yet, in using multiple lasers to produce each individual desired color, it is virtually impossible to produce a coaxial output beam. Thus, alignment problems continue to plague the user.
Prior attempts to produce a multiple color output laser have been less than satisfactory in that specific, selected wavelengths have not been available. Rather, many such lasers produce a broad band of wavelengths which may be only marginally useful. At the same time it was not possible to precisely control the output power of the desired frequencies. Thus, production of a usable multiple frequency output beam has been difficult.
Another problem is the production of undesirable colors. As mentioned above, conventional multiple color lasers produce a wide spectrum of output frequencies, including frequencies which may degrade desired output. In the case of a krypton laser, light of at least seven separate and distinct wavelengths is produced. Many of these wavelengths may not be needed or wanted for a particular application. Accordingly, these wavelengths will reduce the power output of the laser for the desirable wavelengths. This problem is multiplied when multiple lasers are combined.
Accordingly, it would be an advancement in the art to provide a mechanism for producing multiple colors of laser light while avoiding the problems encountered in the art. More particularly, it would be an advancement in the art to provide a single, continuous output, ion laser that was able to produce multiple specific wavelengths of light. It would be a related advantage to produce such an ion laser that did not require complex and tedious alignment procedures in order to produce the desired multiple light wavelengths, in that a multiple color coaxial output beam was produced. It would also be an advancement in the art to produce such a device that was capable of eliminating unwanted light wavelengths. It would be another advancement in the art to produce such an ion laser that was portable and inexpensive to manufacture.
Such an apparatus is disclosed and claimed herein.